1. Field of the Invention
This invention relates generally to passive infrared (IR) detectors and more specifically to an IR location system which uses a plurality of passive IR detectors arranged in specifically designed arcuate arrays and coupled to a local microprocessor to form an IR location system.
2. Description of the Prior Art
It has been known to use detectors sensitive to IR to detect motion. A good discussion of this prior art is provided by Keller-Steinbach, U.S. Pat. No. 4,523,095, where it is explained that a first well known class of prior art applications are IR motion detectors which contain a single IR sensor and multiple lenses each focusing energy from a different location onto the sensor. Thus when an IR emitting body moves, passing from one location (i.e., lens) to another, the intensity read by the sensor varies, thus signaling motion somewhere, (i.e., at a unspecified location within the range of the sensor). As is further discussed in Keller-Steinbach, a weakness in the above class of applications is the frequent occurrence of false alarms, said weakness being eliminated by the use of dual detectors to form a differential sensor which can be balanced to cancel out false alarms due to effects such as ambient temperature, sunlight, heating, cooling, etc.
Other related prior art is provided by Muller, U.S. Pat. No. 4,710,629, which shows another malfunction preventing system; Horii, U.S. Pat. No. 4,912,748, which also uses multiple sensors to prevent errors; Ishikawa et al, U.S. Pat. No. 5,068,537 which uses multiple IR sensors disposed in a straight line to correct errors in a passenger counting system; Guscott, U.S. Pat. No. 5,283,551, which uses an array of IR sensing devices to provide a two dimensional image of an intruder; and Tom, U.S. Pat. No. 5,107,120, which uses multiple adjoining sensors and an arcuate multiple lens to enlarge the field of view of a single sensing device.
In considering the overall objective of an effective intruder detection and alarm system, the actual physical location of the intruder within the area secured by the system is the ultimate objective which the system must achieve in order to be truly effective. Although there is some benefit in knowing that an intrusion has occurred or that an intruder exhibits movement, the real question to be answered in order to determine appropriate action and its urgency is the actual location of the intruder. Thus a need exists for an improved IR detection system which establishes the location of an intruding element quickly and accurately.